In a front jaw according to AT-B-396 337, the bearing part is designed in one piece and is made of a metal, preferably of a cast aluminum. The use of metal is necessary in order to absorb the forces occurring on the toggle levers or to transfer these through the springy force-transfer mechanism to the housing. If the housing is also made of metal, then an insert plate of plastic is used in order to reduce the frictional forces between the bearing part and the housing. This requires both for the manufacture and also for the installation an additional structural part.